Bootstrap gate driver

1. A bootstrap gate driver, comprising: a load indication unit, configured to generate a load indication signal in response to a state of a load; a bootstrap gate-drive unit comprising a bootstrap capacitor, wherein the bootstrap gate-drive unit is configured to drive a switch-transistor circuit in response to an inputted pulse-width-modulation (PWM) signal, and the switch-transistor circuit has a high-side driving path and a low-side driving path; and a drive-control unit, coupled to the load indication unit and the bootstrap gate-drive unit, and configured to enable or disable the high-side driving path in response to the load indication signal, wherein when the load is in a light-loading state, a charging path of the bootstrap capacitor is not established, so as to disable the high-side driving path, wherein when the load is not in the light-loading state, the charging path of the bootstrap capacitor is established, so as to enable the high-side driving path, wherein the load indication unit comprises: a sample circuit, configured to detect the state of the load by a means of voltage/current sensing, so as to provide a detection signal; and a determination circuit, coupled to the sample circuit, and configured to compare the detection signal with a reference signal, so as to generate the load indication signal.

2. The bootstrap gate driver according to claim 1 , wherein the switch-transistor circuit comprises a high-side transistor corresponding to the high-side driving path and a low-side transistor corresponding to the low-side driving path, and the bootstrap gate-drive unit comprises: a high-side driving circuit, coupled to the high-side transistor, and configured to drive the high-side transistor in response to a first control signal related to the inputted PWM signal; a low-side driving circuit, coupled to the low-side transistor, and configured to drive the low-side transistor in response to a second control signal related to the inputted PWM signal, wherein the first and the second control signals are complementary; a bootstrap diode, having an anode coupled to an output of the drive-control unit, wherein a first terminal of the bootstrap capacitor is coupled to a cathode of the bootstrap diode, and a second terminal of the bootstrap capacitor is coupled between the high-side transistor and the low-side transistor; and a signal processing unit, coupled to the high-side driving circuit and the low-side driving circuit, and configured to receive and process the inputted PWM signal, so as to generate the first control signal and the second control signal.

3. The bootstrap gate driver according claim 2 , wherein the high-side driving circuit comprises: a first transistor, having a control electrode receiving the first control signal, a first electrode coupled to the cathode of the bootstrap diode and the first terminal of the bootstrap capacitor, and a second electrode coupled to a gate of the high-side transistor; and a second transistor, having a control electrode receiving the first control signal, a first electrode coupled to the second electrode of the first transistor and the gate of the high-side transistor, and a second electrode coupled to the second terminal of the bootstrap capacitor, a source of the high-side transistor and a drain of the low-side transistor.

4. The bootstrap gate driver according to claim 3 , wherein the low-side driving circuit comprises: a third transistor, having a control electrode receiving the second control signal, a first electrode coupled to a system power, and a second electrode coupled to a gate of the low-side transistor; and a fourth transistor, having a control electrode receiving the second control signal, a first electrode coupled to the second electrode of the third transistor and the gate of the low-side transistor, and a second electrode coupled to a source of the low-side transistor.

5. The bootstrap gate driver according to claim 4 , wherein the first to the fourth transistors are bipolar junction transistors (BJTs).

6. The bootstrap gate driver according to claim 5 , wherein the first and the third transistors are NPN-type BJTs, and the second and the fourth transistors are PNP-type BJTs.

7. The bootstrap gate driver according to claim 4 , wherein the drive-control unit comprises: a fifth transistor, having a control electrode receiving the load indication signal, and a first electrode coupled to a ground potential; and a sixth transistor, having a control electrode coupled to a second electrode of the fifth transistor, a first electrode coupled to the system power, and a second electrode coupled to the anode of the bootstrap diode, wherein the second electrode of the sixth transistor is served as the output of the drive-control unit.

8. The bootstrap gate driver according to claim 7 , wherein the drive-control unit further comprises: a current-limiting resistor, coupled between the second electrode of the fifth transistor and the control electrode of the sixth transistor.

9. The bootstrap gate driver according to claim 7 , wherein the fifth transistor is an N-type transistor, and the sixth transistor is a PNP-type BJT.

10. The bootstrap gate driver according to claim 7 , wherein: when the load is in the light-loading state, the load indication signal is in a low level, such that the fifth and the sixth transistors are turned off, and then the charging path of the bootstrap capacitor is not established, so as to disable the high-side driving path; and when the load is not in the light-loading state, the load indication signal is in a high level, such that the fifth and the sixth transistors are turned on, and then the charging path of the bootstrap capacitor is established, so as to enable the high-side driving path.

11. The bootstrap gate driver according to claim 2 , wherein the signal processing unit comprises: a first series-connected level-shift module and logic module, configured to receive and process the inputted PWM signal, so as to generate the first control signal; and a second series-connected level-shift module and logic module, configured to receive and process the inputted PWM signal, so as to generate the second control signal.

12. The bootstrap gate driver according to claim 2 , wherein the high-side transistor and the low-side transistor are N-type power transistors.

13. The bootstrap gate driver according to claim 1 , wherein the bootstrap gate driver is at least suitable for a voltage converter.

14. The bootstrap gate driver according to claim 13 , wherein the voltage converter comprises a boost converter.